1. The Impact of the Galactic Center Arches Cluster: Radio & X-ray Observations
Cornelia C. Lang
University of Iowa
collaborators:
W.M. Goss, K.E. Johnson, M. Morris,
L.F. Rodriguez, Q.D. Wang &
F. Yusef-Zadeh
GC region (Sagittarius) is obscured by
~30 visual magnitudes of extinction
– no optical, UV; we rely on near-IR,
radio and X-ray observations

2. Outline Arches Cluster: Radio results Arches Cluster: X-ray results
Ionization and kinematics of dense molecular clouds
Detections of individual stellar winds in the cluster
Arches Cluster: X-ray results
Arches cluster is one of the brightest sources in the GC
Point-like X-ray sources and diffuse emission features*
Arches Cluster: Xraydio results
Nonthermal diffuse radio emission
Nonthermal point-like radio emission
Nature of the diffuse 6.4 keV emission
Galactic Center: Xraydio results
several nonthermal radio and X-ray features (SNR? NTFs?)
diffuse 6.4 keV emission/molecular gas in GC: Casey Law poster

3. Yusef-Zadeh, Morris & Chance (1984)
Arches Region: best example of interplay between GC components
VLA 20 cm
Yusef-Zadeh, Morris & Chance (1984)
Lang et al. (1999)
GCs are known to have
dense concentrations of
- massive stars
- molecular clouds
- ionized gas
- magnetic fields
- hot ISM
- SMBH
the *interplay* between
these components which
gives rise to
ENERGETIC
EPISODIC
activities
Sickle & Pistol
H II regions
Arched Filaments
H II Regions + +
25’~60 pc
Sgr A complex +

4. Radio: Ionization & Kinematics of Arches region
VLA H92a velocity distribution
H92a line
CS(2-1) line
(Lang, Goss & Morris 2001)
+20 to -60 km/s
(Lang, Goss & Morris 2001)
Arches cluster can ionize edge of cloud
NLyc(cluster) ~ 4x1051 ph. s-1
NLyc (radio cont.) ~ 3x1050 ph. s-1
Arches cluster could be ~20 pc
away from molecular cloud
- molecular cloud on peculiar orbit around GC
- cluster not likely to have been born from
this particular cloud = passerby
- large velocity difference between them:
Vgas = +20 to -60 km/s
Vstars = +95 km/s (Figer et al. 2002)

5. Radio: Stellar Winds in the Arches Cluster
9 sources detected at
4.9, 8.3, 22, 43 GHz
use high resolution to study
radio emission from stellar winds
 ~ +0.3 to +0.9
 ~ -0.7 (AR6)
+ represent near-IR
mass-losing sources
(Nagata et al. 95; Cotera et al. 96)
“V” sources show
10-30% variability
between epochs
high mass loss rates
~ 3 – 17 x 10-5 Mo yr-1
(no clumping corrections)
HST/NICMOS (Figer et al. 1999)
combination of 1999 (Lang et al. 2001b) and 2002 observations

6. Chandra X-ray Observations: Arches Cluster
275 pc ~ 900 ly
Galactic Center Survey (Wang, Gotthelf & Lang 2002)
100 pc ~325 ly
Arches Cluster
X-ray: red 1-3 keV, green 3-5 keV, blue 5-8 keV
Arches cluster is one of brightest X-ray sources in the GC region

7. X-ray: Point like Sources in the Arches
Arches Cluster
3 X-ray point sources in cluster as
well as considerable diffuse emission
(Yusef-Zadeh et al. 2002)
point sources fit with two temperature model T ~ 0.7 keV and T~ 5 keV
Lx ( keV) ~ 1-2 x 1035 erg/s
2 centrally located X-ray sources are
coincident with
- late type Of/Wolf-Rayet stars
- radio continuum sources
interpretation of X-ray sources:
- colliding wind binary sources
- similar to NGC3603, R136
Law & Yusef-Zadeh 2003
contours: 1-10 keV emission (Wang, Gotthelf & Lang 2002)
colorscale: NICMOS near-IR image (A.Cotera)

8. X-ray: Diffuse X-ray emission in the Arches
Diffuse X-ray emission prominent
in the Arches cluster
Lx ( keV) ~ 5 x 1035 erg/s for
all components of the Arches
“Cluster wind” – the resulting outflow
of shock-heated gas caused by the
collisions of 10’s of stellar winds
Canto et al. (2000) predict such a wind
and simulations by Raga et al. (2001)
Interesting feature in the spectrum
of the diffuse emission: 6.4 keV line
(after point sources are subtracted)
 more on this shortly
Arches Cluster
Diffuse Emission
Law & Yusef-Zadeh 2003
(Yusef-Zadeh et al. 2002)
contours: 1-10 keV emission (Wang, Gotthelf & Lang 2002)
colorscale: NICMOS near-IR image (A.Cotera)

9. Xraydio: Nonthermal Diffuse Radio Emission
90 cm
20 cm
Nonthermal radio source associated with Arches
 VLA detection of Arches at 90 cm
 surprising discovery b/c much of surrounding radio emission becomes optically thick at 90 cm - nonthermal
 interpreted as acceleration due to shocks from wind-wind collisions in the cluster core (outflow)
Yusef-Zadeh et al. 2003

10. Xraydio: Nonthermal Radio Stellar Wind Emission
Several Arches radio wind
sources show flattened or
nonthermal (NT) spectral
index
 NT wind component
 30-60% of winds have
NT component (Leitherer et al. 1997)
due to wind-wind collisions
in a binary system
VLBA radio observations
of Arches cluster might
show compact NT emission
(proposed) & confirm
- NT component
- stars are binaries!

11. Xraydio: Correlation between 6
Xraydio: Correlation between 6.4 keV emission and molecular gas near Arches
CS (2-1) OVRO ~8” x 4”
greyscale: CS (2-1) IRAM
contours; 6.4 keV Chandra
crosses: Arches cluster stars

12. Xraydio: Other GC sources of both X-ray & Radio
20 cm VLA
Wang, Lu & Lang 2003
Lu, Wang & Lang 2003
Lu, Wang & Lang 2003

13. Conclusions
Arches Cluster
- responsible for ionizing cloud edges
- young stars losing mass at high rates, collisions of winds
- collective expanding: ‘cluster wind’
- X-ray sources may illuminate the molecular gas (6.4 keV) near Arches
The Arches Cluster environment is similar to NGC3603 and 30 Dor
GC region is much more completely understood by incorporating massive
Stars and their influence
Overall diffuse hot emission in GC (traced by X-rays) likely to arise from massive star activities – SNR, winds
is our Galactic Center unique?
- identify and compare similar structures, interplay in nearby galaxies

14. Massive star activities driving energetics in the GC
Arches
Cluster
MSX Mid-IR 25 mm
Wang, Gotthelf & Lang 2002
 Massive star forming activites drive energetics in GC
30 pc
Radio Arc
Region
Sgr B2